Whip the first four ingredients together.
Drain sauerkraut and rinse with cold water, then drain again.
Saute onion in the butter until lightly browned.
Spread half the potato in a greased 1 1/2 quart casserole.
Sprinkle with half the cheese and spread with sauerkraut and onion mixture.
Cover with remaining potato.
Pour boiling water over sausages and bring to a boil, then drain.
Arrange sausages like the spokes of a wheel over potato topping.
Bake at 375F for 15 minutes, then turn sausages over and continue baking for 10 minutes.
Sprinkle with remaining cheese and bake until melted.